Heretofore, several methods have been known for making metal powder directly from a melt of the metal by using rotation; such as a method in which a melt of metal in a fixed crucible is dropped through a nozzle bored at its lower portion toward the central portion of a rotary disk so that the molten metal is centrifugally dispersed and formed into powder particles, a method that uses a specimen rod of metal as an electrode so as to melt a part of it with a plasma arc or the like while rotating it so as to disperse the molten metal for producing the metal powder particles, and a method of forming metal powder particles by jetting melt of the metal into a rotating liquid coolant for causing collision of the jetted melt with the coolant.
In the first two methods using the rotary disk and the rotating electrodes, respectively, an annular belt of the melt is centrifugally formed on the rotary disk or the outer surface of the revolving metal rod, and metallic droplets are dispersed from the annular belt of the melt. Thus, a very high revolving speed is required in order to produce minute droplets. Accordingly, the conventional methods have shortcomings in that minute powder particles are difficult to produce because the revolving speed of the rotary disk and the revolving rod is limited from the standpoint of the safety of rotating device, and that, when the coolant is an inert gas, its cooling speed is not so high and a long flying distance is required for the droplets to solidify, and the apparatus for making the metal powder tends to become large and deposition of the powder metal on the apparatus wall tends to increase. A method, in which melt of metal in a fixed crucible is jetted in an atomized fashion by gas pressure into a rotary drum containing water, has excellent property in producing fine powder particles but has a shortcoming in that the surface of powder particles tends to be contaminated by the liquid coolant and a large amount of powder particle deposit on the outer wall.
There is a method in which a melting vessel and a liquid coolant tank are rotated simultaneously while allowing variation of the revolving speed ratio thereof and changing of the revolving directions, and the melt in the melting vessel is jetted centrifugally into the liquid coolant in the cooling tank so as to produce metal powder particles. Such a method also has excellent property in producing fine powder particles but has shortcomings in that contamination of the powder particles cannot be avoided and that it is not suitable for metals with a high melting point.